PROJECT SUMMARY/ABSTRACT Obesity affects nearly 40% of reproductive-aged women in the United States (U.S.) and is associated with multiple perinatal complications. It has been hypothesized that the increasing prevalence of obesity during pregnancy may be partly responsible for the high rates of maternal mortality in the U.S. However, the evidence of the association between maternal body mass index (BMI) and maternal mortality, and the more common ?near miss? cases of severe maternal morbidity (SMM) is conflicting and limited by the lack of assessment of these outcomes beyond the delivery hospitalization, despite the fact that a significant proportion of pregnancy-related deaths occur after hospital discharge. Our study will utilize an innovative approach that assesses not only maternal mortality but also SMM through one year following delivery. We will test the hypothesis that the risk of SMM and/or mortality occurring between 20 weeks of gestation and one year postpartum is higher among women with obesity compared to women with a normal pre-pregnancy BMI. To test this hypothesis, we will utilize existing linked Ohio statewide datasets that include birth, fetal death, and maternal death records, the Ohio Pregnancy- Associated Mortality Review information, and an Ohio Medicaid administrative database. In Aim 1, we will examine the association between pre-pregnancy maternal BMI and SMM and/or mortality through one year after delivery. We will use causal inference methods to further assess this relation focusing on hypertensive disorders and diabetes as possible mediators. In addition, we will explore whether maternal obesity contributes to the racial disparities in SMM and mortality previously observed. The purpose of Aim 2 is to develop a clinical tool, which can be used following the delivery hospitalization, to identify women with obesity who are at highest risk for SMM and mortality using predictive modeling. The postpartum period is increasingly being recognized as a vulnerable time for women, but engagement in care following delivery is generally poor. Evidenced-based risk stratification could help guide the development of postpartum care models that optimize care and provide support to women who are at greatest risk for SMM and mortality. This research will expand our understanding of the relation between obesity and SMM and mortality.